The document discusses online patching, also called hot patching, in Oracle 11g. It allows installing, enabling, or disabling a fix or diagnostic patch while the database instance remains online. This avoids downtime for maintenance and allows applying patches. Only small, low-complexity patches like diagnostic patches or small bug fixes can be applied online. Hot patching requires additional memory usage that depends on the patch size and number of processes in the instance. The document provides an example patch number that supports online patching in Oracle 11g and discusses testing online patching.